1. Field of the Invention
The present invention relates to a moving object with at least two energy output sources including fuel cells incorporated therein, a driving apparatus for the moving object, and a method of controlling the moving object.
2. Description of the Related Art
Hybrid vehicles with an engine and a motor mounted thereon have been proposed recently. In one form of the hybrid vehicle called a parallel hybrid vehicle, the power of both the motor and the engine is output to a drive shaft. The parallel hybrid vehicle has the engine and a battery as energy output sources to produce mechanical and electrical power to rotate the drive shaft. The parallel hybrid vehicle may run only with the power from the engine or from the battery. Proper conditional use of these two energy output sources enables the engine to operate in an efficient operating range. The motor may also act as a generator to convert the mechanical power of the driving shaft into electric power while causing a braking force to the driving shaft. The regenerative braking by the motor recovers the kinetic energy of the vehicle to charge the battery. Because of these functions, the parallel hybrid vehicle has excellent fuel consumption and environmental properties.
Another form of the hybrid vehicle is called a series hybrid vehicle. The series hybrid vehicle runs with power from a motor connected with the drive shaft. The engine is disposed separately from the drive shaft and drives a generator to generate electric power. The motor is driven with at least either one of the electric power generated by the generator and the electric power supplied from a battery. The series hybrid vehicle also has the two energy output sources of the engine and the battery. Proper combinational use of these two energy output sources ensures the excellent fuel consumption and environmental properties.
Some vehicles with fuel cells mounted thereon as one of energy output sources have been proposed as one type of the parallel hybrid vehicle (for example, a vehicle disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 3-148330). The fuel cells oxidize hydrogen, or fuel, to generate electric power. The exhaust from the fuel cells is water vapor and does not contain any harmful components. The fuel cells accordingly have extremely excellent environmental properties. Some types of fuel cells utilize a hydrogen rich gas generated by reforming of a fuel, such as methanol. Hybrid vehicles having these fuel cells and a gasoline engine are provided with a plurality of fuel reservoirs, in which methanol and gasoline are separately stored.
The fuel cell technology is being under rapid development these days. There is accordingly no sufficient discussion on the optimum combination of the output characteristics of the fuel cells with those of another energy output sources such as a heat engine. The fuel cells generate electrical energy like secondary batteries, but they are irreversible energy output sources. The secondary battery is rechargeable even in the course of a drive of the hybrid vehicle. The fuel cells, on the other hand, do not recover their power generation ability without an external supply of fuel. Another disadvantage of the fuel cells is a poor response.
Hybrid vehicles with the fuel cells have been proposed to combine the advantages of the conventionally used engine with these of the fuel cells. In the proposed hybrid vehicles with the fuel cells, however, the effective use of the fuel cells has not been fully considered by taking into account the above characteristics.
In the proposed hybrid vehicles with the fuel cells mounted thereon, the fuel cells are used only in a limited manner and not fully utilized. The favorable fuel consumption and the other advantages of the hybrid vehicle have not been fully utilized. Sufficient warming up is generally required in the process of power generation by the fuel cells. The fuel cells accordingly have a poor response to a requirement of power generation. There has been no sufficient discussion on the method of compensating for the poor response and outputting the required electric power.
In the proposed hybrid vehicles with the fuel cells mounted thereon, there has been substantially no discussion on the selective use of energy output sources at a drive in a specific condition that is different from a normal drive. There has also been substantially no discussion on the technique of utilizing the characteristics of the fuel cells as an electric power supply of high efficiency and excellent environmental properties, so as to improve the facility of the hybrid vehicle.
In the vehicle with a plurality of energy output sources requiring different types of fuels, such as fuel cells and a gasoline engine, it is required to supply the corresponding fuels to the respective fuel reservoirs or tanks without any confusion. No simple structure, however, has been proposed to prevent confusion between the plurality of fuels supplied.
The conventional vehicles have another problem relating to vibration damping of the engine as discussed below. The engine generally has a pulsation or variation in its output torque. In a vehicle with a motor in addition to the engine as a mechanism to output a torque to the drive shaft, the motor can compensate for a variation in the torque output from the engine to the drive shaft. There has been no sufficient discussion on the effective use of the fuel cells as the electric power supply of the motor in the torque control.
When the engine torque is greater than a required torque, the motor carries out regenerative operation to give a load, thereby attaining the required torque output. When the engine torque is less than the required torque, on the other hand, the motor carries out power operation to attain the required torque output. The torque control is generally accompanied by extraction and supply of electric power from and into the motor. The conventional technique implements such control with the secondary battery. The fuel cells are the power generator unit that carries out only power generation, and can not replace the secondary battery.
The torque control technique with the secondary battery, however, has a problem that the extraction and supply of electric power from and into the motor are difficult to balance, and thereby the electric power of the secondary battery is often consumed excessively. This is ascribed to a conversion loss between the mechanical power and the electric power due to the charge and discharge efficiencies of the secondary battery.
One proposed technique for compensating the conversion loss includes the use of another electric power supply. The fuel cells may be used as such an electric power supply for compensation. While the motor carries out power operation for the vibration damping, this proposed technique restricts the discharge of the secondary battery by the amount of the electric power previously regenerated and causes the fuel cells to compensate for an insufficiency of electric power. The electric power supplied from the secondary battery, however, has a low efficiency due to the losses in the charging and discharging process. The primary use of such electric power results in lowering the energy efficiency in the vibration damping. The use of the fuel cells for the purpose of compensation does not effectively draw the advantages of the fuel cells having the high efficiency of power generation.
The issues discussed above arise not only in the hybrid vehicles but in any moving objects having a plurality of energy output sources including fuel cells.